Coating compositions for plastic substrates

ABSTRACT

The present invention provides radiation-curable compositions for coating plastic substrates, wherein the compositions, after cure, have a combination of sufficient adhesion, flexibility, and hardness. The compositions include: (a) at least one component comprised of a metal oxide bonded to an organic compound, said organic compound having (i) a radiation curable group; and 
 
(ii) a group represented by the following formula (1)  
                 
wherein X represents an amine (NH), oxygen (O), or sulfur (S) radical; and Y represents an oxygen (O), or sulfur (S) radical; (b) a poly(meth)acrylate compound; and (c) an adhesion promoter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.09/951,777, filed Sep. 14, 2001, and further claims the benefit ofpriority to U.S. provisional application Ser. No. 60/232,427, filed Sep.14, 2000, both of which are hereby incorporated in their entirety byreference.

FIELD OF THE INVENTION

The present invention relates to radiation curable compositions, tocoatings formed by curing these compositions, and to articles comprisingsuch coatings. An aspect of the invention concerns the use of thepresent compositions to form protective coatings on substrates includingfor example display monitors (like flat screen computer and/ortelevision monitors such as those utilizing technology discussed in, forexample, U.S. Pat. Nos. 6,091,184 and 6,087,730 which are both herebyincorporated by reference), optical discs, smart cards and the like.

BACKGROUND OF THE INVENTION

There is great interest in the development of plastic substrates for,for instance, LCD (liquid crystal display) and OLED (organic lightemitting diode) display applications. Plastic substrates are light andtough, and comparatively easy to shape. However, plastics are typicallyrelatively soft and, thus, there is the need to deposit a protectivelayer on the exposed surface of the plastic. Such protective layers arepreferably relatively hard (to provide, e.g., scratch resistance) yetalso substantially flexible. In addition, such layers should adhere wellto the surface they are coated on.

SUMMARY OF THE INVENTION

The present invention provides compositions that, after cure, adherewell to plastic substrates and provide a flexible material having ahard, scratch resistant surface. The compositions comprise (i) a metaloxide bound to an organic compound having a radiation-curable group,(ii) a poly(meth)acrylate compound, and (iii) an adhesion promoter.

DESCRIPTION OF THE INVENTION

It is to be understood that the term polynorbornene herein refers to apolymer wherein at least 10 wt %, relative to the total weight of thepolymer, results from the polymerization of norbornene monomers, morepreferably at least 50 wt %, even more preferably at least 80 wt %, andmost preferably at least 95 wt % results from the polymerization ofnorbornene monomers. Polynorborene may be a random copolymer, a blockcopolymer, a homopolymer or a polymer resulting from three or moremonomers. Examples of polynorbornenes are, for instance, described inU.S. Pat. Nos. 5,468,819; 5,569,730; 5,571,881; 5,677,405; 5,741,869;and RE 34,638; which six patents are hereby incorporated in theirentirety by reference. “(Meth)acrylate” refers in this application to“acrylate and/or methacrylate”.

The present invention concerns compositions for coating a plasticsubstrate, wherein the compositions comprise a component (A) comprisedof a metal oxide bonded to an organic compound, wherein the organiccompound has

-   -   (i) a radiation curable group; and    -   (ii) a group represented by the following formula (1)    -   wherein    -   X represents an amine (NH), oxygen (O), or sulfur (S) radical;        and    -   Y represents an oxygen (O) or sulfur (S) radical;    -   wherein a coating formed by curing a 25 micron thick layer of        said composition on a 0.1 mm thick polynorbornene substrate has        -   (a) sufficient adhesion to said plastic substrate;        -   (b) a pencil hardness of 1B or higher; and        -   (c) sufficient flexibility.

Suitable examples of the component comprised of a metal oxide bonded toan organic compound are, for instance, set forth in U.S. Pat. No.6,160,067 to Eriyama et al, which is hereby incorporated in its entiretyby reference. Preferably, the metal oxide comprises at least one metalselected from the group consisting of silicon, aluminum, zirconium,titanium, zinc, germanium, indium, tin, antimony, and cerium. Theorganic group preferably comprises a radiation-curable group that isethylenically unsaturated, for instance a (meth)acrylate group,preferably an acrylate group.

The present compositions preferably comprise at least 20 wt/o, relativeto the total weight of the composition, of the component comprised of ametal oxide bonded to an organic compound, more preferably at least 35wt %, and most preferably at least 50 wt %. The present compositionspreferably comprise less than 95 wt %, more preferably less than 85 wt%, of the component comprised of a metal oxide bonded to an organiccompound.

Preferably, the present compositions comprise at least onepoly(meth)acrylate monomer, i.e. a monomer comprising at least twoacrylate or methacrylate groups, and more preferably at least twopoly(meth)acrylate monomers. The poly(meth)acrylates may be alkoxylated,for instance ethoxylated or propoxylated. Preferably the compositioncomprises a tri(meth)acrylate, more preferably an alkoxylatedtri(meth)acrylate, most preferably an ethoxylated tri(meth)acrylate. Anexample of a preferred ethoxylated tri(meth)acrylate is, for instance,ethoxylated trimethylolpropane triacrylate. Commercial examples ofethoxylated trimethylol propane triacrylate include SR 502 fromSartomer, which is an ethoxylated (9) trimethylol propane triacrylate.Examples of non-alkoxylated tri(meth)acrylates that can be used in thepresent invention include, for instance, tris(2-hydroxyethyl)isocyanurate triacrylate, which is commercially available from,for instance, Sartomer as SR-368.

Examples of other preferred poly(meth)acrylate monomers includepenta(meth)acrylates. Preferred penta(meth)acrylates include, forinstance, dipentaerythritol monohydroxypenta acrylate. Commercialexamples of such a pentacrylate include SR-399 from Sartomer. Preferablythe compositions of the present invention comprise both atri(meth)acrylate and a penta(meth)acrylate.

The present compositions may also comprise mono(meth)acrylate monomersas well as other radiation curable monomers such as N-vinyl functionalmonomers.

Preferably, the present compositions comprise monomers which not onlycomprise one or more (meth)acrylate groups, but also other functionalgroups such as one or more hydroxy groups and/or one or more carboxylicacid groups.

Preferably, the present compositions comprise, relative to the totalweight of the composition, 5-50 wt % of (meth)acrylate-functionalmonomers (preferably poly[meth]acrylate monomers), more preferably 10-35wt %, most preferably 15-25 wt %.

Preferably, the present compositions comprise 1-25 wt %, relative to thetotal weight of the composition, of monomers comprising 3 (meth)acrylategroups, more preferably 5-25 wt %. Preferably, the present compositionscomprise, relative to the total weight of the composition, 5-25 wt % ofmonomers comprising 5 (meth)acrylate groups, more preferably 10-20 wt %.

If the composition comprises both a penta(meth)acrylate compound and atri(meth)acrylate compound, the weight ratio of penta(meth)acrylatecompounds in the composition to tri(meth)acrylate compounds in thecomposition is preferably below 5, more preferably below 3, and mostpreferably below 2.

The present compositions preferably comprise an adhesion promoter.Preferred adhesion promoters include silane adhesion promoters, forinstance polyalkoxysilanes such as gamma-mercaptopropyltrimethoxysilaneand methacryloxypropyl trimethoxy silane. Methacryloxypropyl trimethoxysilane is most preferred, for instance because it tends to have bettershelf life than gamma-mercaptopropyl trimethoxy silane. Preferably thepresent compositions comprise, relative to the total weight of thecomposition, at least 1 wt % of adhesion promoter, more preferably atleast 3 wt %, and most preferably at least 5 wt %. Generally, thepresent compositions will comprise less than 25 wt % of adhesionpromoter.

Although generally not preferred, the present compositions may compriseany suitable epoxy-functional compound. Examples of suitableepoxy-functional compounds include bisphenol A diglycidyl ethers, epoxynovolaks, and cycloaliphatic epoxides. Preferred cycloaliphatic epoxidesinclude those comprising one or more, preferably two, cyclohexene oxidestructures, such as 3,4-epoxycyclohexyl-methyl-3,4-epoxycyclohexanecarboxylate. Preferably, the present compositions comprise less than 30wt % of epoxy-functional compounds, more preferably less than 15 wt %,and most preferably the present compositions are absent epoxy-functionalcompounds.

The present compositions may further comprise several additives, such asone or more photoinitiators (preferably at least two photoinitiators).

The coating thickness of the composition on the substrate, after cure ofthe composition, is preferably in the range of 1-100 microns, morepreferably 5-50 microns.

Preferably, the pencil hardness of the compositions, after cure, is atleast B, more preferably at least HB, and most preferably at least H.

Furthermore, a 5-10 micron thick cured layer of the present compositionspreferably has a transparency of at least 65% for light having awavelength of 400 run, more preferably at least 75%, and most preferablyat least 90%.

The present compositions have, after cure, sufficient adhesion toplastic substrates. Preferably the compositions have an adhesion valueof at least 1, more preferably at least 3, as measured according to ASTMD3359.

The present compositions are, after cure, sufficiently flexible.Preferably, the compositions exhibit a flexibility such that less than10 cracks, more preferably less than 5 cracks, and most preferably nocracks, are visible in a 5-10 micron thick cured layer of thecomposition, wherein the composition is coated on a plastic substrate(length 20 cm, width 5 cm, and thickness 100 microns) and wound around arod of 3.10 mm diameter with the plastic facing the surface of the rodand, consequently, the coating (cured composition) facing away from therod.

The present compositions may be used as coating compositions. Forinstance, the present compositions may be used to coat substrates.Suitable substrates to be coated include organic substrates. Organicsubstrates are preferably polymeric (“plastic”) substrates, such assubstrates comprising polynorbornene, polyethyleneterephtalate,polymethylmethacrylate, polycarbonate, polyethersulphone, polyimide,and/or polyethernaphtalene. Particularly preferred substrates includepolynorbornene substrates and polyimide substrates.

The substrates may be pre-treated prior to coating with the presentcompositions. For instance, the substrates may be subjected to corona orhigh energy treatment. The substrates may also be chemically treated,such as by emulsion application.

Preferably, the substrate comprises functional groups such as hydroxygroups, carboxylic acid groups and/or trialkoxysilane groups such astrimethoxysilane. The presence of such functional groups may improveadhesion of the coating to the substrate.

There is no specific limitations to the method for preparing thecrosslinkable particles (A) used in the present invention. Methods forpreparing the particles are disclosed in, for instance WO 00/47666,which is hereby incorporated in its entirety by reference. A method ofreacting the above-mentioned specific organic compound and oxideparticles can be given as an example:

Oxide particles (A₁) are known to have moisture on the surface ofparticles as adsorption water under usual storage conditions. Inaddition, components which react with a silanol group-forming compoundsuch as a hydroxide, hydrate, or the like are presumed to be present atleast on the surface of the oxide particles. Therefore, thecrosslinkable particles (A) can be produced by mixing the silanolgroup-forming compound and oxide particles (A₁), and heating the mixturewhile stirring. It is preferable that the reaction be carried out in thepresence of water to efficiently bind the silanol group-forming sitepossessed by the specific organic compound (A₂) and the oxide particle(A₁). However, water is not required when the specific organic compound(A₂) and (optionally) compound (A₃) possess silanol groups. Therefore,the crosslinkable particles (A) can be prepared for example by a methodwhich includes at least the operation to blend the oxide particles (A₁),the specific organic compound (A₂) and (optionally) compound (A₃).

The crosslinkable particles may be prepared, for example, by a two stepprocess. The first step involving hydrolyzing the compound (A₂) andbonding the hydrolyzed compound to oxide particles (A₁). And a secondstep of hydrolyzing the compound (A₃) and bonding the particles obtainedin the first step to the hydrolyzed compound obtained from compound(A₃). Hydrolysis may be omitted, when the compound (A₂) and compound(A₃) are not silanol group-forming compounds, but silanolgroup-containing compounds.

First Step

The first step comprises reacting a mixture of oxide particles (A₁) anda solvent or oxide particles (A₁) dispersed in a solvent with thecompound (A₂) to bond oxide particles (A₁) and the compound (A₂) (suchbonded particles may be hereinafter referred to as “intermediateparticles”). Specifically, the oxide particles (A₁), the compound (A₂),and water are blended under the following conditions to produce theintermediate particles.

Here, p-methoxyphenol for example, may be added as a thermalpolymerization inhibitor. The same solvent as used as a dispersionmedium for the solvent dispersion sol of the oxide particles (A₁) can beused as a solvent.

The temperature for the reaction may be between the temperature at whichthe solutes do not precipitates and the boiling point of the solvent,with the preferable temperature range being from 0 to 150° C.

There are no specific restrictions to the manner of stirring inasmuch asthe mixture can be homogeneously mixed.

The reaction is carried out usually in an atmosphere of a dry gas suchas nitrogen or air, with dry air being preferred. A reaction time withinwhich the reaction is sufficiently completed, for example, from 5minutes to 24 hours, and preferably from one hour to 8 hours, can beapplied.

Second Step

The second step comprises reacting the intermediate particles producedin the first step and the compound (A₃), thereby obtaining crosslinkableparticles in which the intermediate particles are bonded with thecompound (A₃). Specifically, the intermediate particles, the compound(A₃), and water are mixed under the following conditions to producecrosslinkable particles.

The temperature for the reaction may be between the temperature at whichthe solutes do not precipitates and the boiling point of the solvent,with the preferable temperature range being from 0 to 150° C.

There are no specific restrictions to the manner of stirring inasmuch asthe mixture can be homogeneously mixed.

The reaction is carried out usually in an atmosphere of a dry gas suchas nitrogen or air, with dry air being preferred. A reaction time withinwhich the reaction is sufficiently completed, for example, from 5minutes to 24 hours, and preferably from one hour to 8 hours, can beapplied.

The crosslinkable particles can be obtained by bonding the oxideparticles (A₁), compound (A₂), and compound (A₃) through first andsecond steps in this manner.

As mentioned above, it is desirable to produce the crosslinkableparticles by first treating with the compound (A₂), followed by atreatment with the compound (A₃).

Taking the case using silica particles as the oxide particles (A₁) as anexample, both impaired storage stability and inferior coating surfacesare associated with dispersion stability of the crosslinkable particlesin the composition. Because the compound (A₂) is relatively bulky, thetreatment only with the compound (A₂) cannot completely restrain thesilanol group on the surface of particles from condensing after thetreatment. However, successive treatment with the compound (A₃) with arelatively small molecular size is presumed to effect a smooth bondingon the surface of the particles, whereby the remaining silanol groupscan be reduced more efficiently, resulting in improved dispersionstability of particles.

If the treatment with the compound (A₃) is carried out simultaneouslywith or prior to the treatment with the compound (A₂), dispersionstability of particles may be impaired, which results in impairedstorage stability of the coating material and an inferior coating filmappearance.

The amount of each of the compound (A₂) and the compound (A₃) bonded tothe oxide particles (A₁) is 0.01 wt % or more, preferably 0.1 wt % ormore, and particularly preferably 1 wt % or more, in the crosslinkableparticles. If the amount of either the compound (A₂) or the compound(A₃) bonded with the oxide particles (A₁) is less than 0.01 wt %,dispersibility of the crosslinkable particles in the composition may beinsufficient, which may result in cured products with insufficienttransparency and scratch resistance. The amount of the oxide particles(A₁) used in the raw materials for preparing the crosslinkable particlesis preferably from 5-99 wt %, and more preferably from 10-98 wt %.

The method for preparing the crosslinkable particles will now bedescribed in more detail for the case where the alkoxysilane compoundshown by the following formula (2) is used as a silanol group-formingcompound.

wherein

-   R¹ and R² individually represent a hydrogen atom or an alkyl group    or aryl group having 1-8 carbon atoms;-   m represents 1, 2, or 3;-   R³ represents a divalent organic group having a C₁-C₁₂ aliphatic or    aromatic structure which may include a linear, branched, or cyclic    structure;-   R⁴ represents a divalent organic group;-   R⁵ represents an organic group of an (n+1) valence;-   Z is a monovalent organic group having a polymerizable unsaturated    group in the molecule which causes an inter-molecular cross-linking    reaction in the presence of active radicals; and-   n represents an integer from 1 to 20.

The amount of water consumed in the hydrolysis of the alkoxysilanecompound in the preparation of the crosslinkable particles may be theamount sufficient to hydrolyze at least one alkoxy group on the siliconatom in one molecule. Preferably, the amount of water which is added orpresent during the hydrolysis reaction is one third (⅓) or more of thenumber of mols of the total alkoxy groups on the silicon atoms of thealkoxysilane compound, with particularly preferable amount being from ½to 3 times of the number of mols of the total alkoxy groups. The productobtained by mixing the alkoxysilane compound and the oxide particles(A₁) under the conditions where no moisture is present is a productwherein the alkoxysilane compound has physically absorbed on the surfaceof oxide particles (A₁). The cured products made from the compositionwhich includes such crosslinkable particles can exhibit onlyinsufficient hardness and scratch resistance.

The methods which can be selected for the preparation of crosslinkableparticles (A) include a method of separately hydrolyzing theabove-mentioned alkoxysilane compound, and mixing the hydrolyzed productwith a powder of oxide particles or a solvent dispersion sol of oxideparticles with heating and stirring; a method of carrying out thehydrolysis of the alkoxysilane compound in the presence of the oxideparticles; and a method of treating the surface of the oxide particlesin the presence of, for example, (D) the polymerization initiator andthe like. Among these, the method of hydrolyzing the alkoxysilanecompound in the presence of oxide particles is preferable. The treatmentfor the preparation of the crosslinkable particles (A) is carried out ata temperature from 0 to 150° C., preferably from 20 to 100° C. Thetreating time is usually from 5 minutes to 24 hours.

When oxide particles in the form of a powder are used in the preparationof the crosslinkable particles (A), an organic solvent may be added toensure a smooth and homogeneous reaction with the alkoxysilane compound.The same solvents as used as the above-mentioned dispersion medium forthe solvent dispersion sol of oxide particles can be used as such anorganic solvent. There are no specific limitations to the types of thesesolvents, in as much as a smooth and homogeneous reaction is ensured.

When a solvent dispersion sol is used as the raw material for thecrosslinkable particles (A), the crosslinkable particles (A) can beprepared by a process comprising at least a step of mixing the solventdispersion sol and the specific organic compound. Here, an organicsolvent which is mutually soluble with water can be added to ensurehomogeneity in the initial stage of the reaction and smooth reaction.

Moreover, an acid, salt, or base may be added as a catalyst toaccelerate the reaction to produce the crosslinkable particles (A).Given as examples of the acid are inorganic acids such as hydrochloricacid, nitric acid, sulfuric acid, and phosphoric acid, organic acidssuch as methanesulfonic acid, toluenesulfonic acid, phthalic acid,malonic acid, formic acid, acetic acid, and oxalic acid, as well asunsaturated organic acids such as methacrylic acid, acrylic acid, anditaconic acid. As examples of the salt, ammonium salts such astetramethylammonium chloride and tetrabutylammonium chloride can begiven. Given as examples of the base, aqueous ammonia; primary,secondary, or tertiary aliphatic amines such as diethylamine,triethylamine, dibutylamine, and cyclohexylamine; aromatic amines suchas pyridine; sodium hydroxide, potassium hydroxide; as well as tertiaryammonium hydroxides such as tetramethylammonium hydroxide,tetrabutylammonium hydroxide, and the like. Among these, preferablecatalysts are acids such as organic acids and unsaturated organic acids,and bases such as tertiary amines and quaternary ammonium hydroxide. Theamount of these acids, salts, or bases to be added is preferably from0.001 to 1.0 part by weight, and more preferably from 0.01 to 0.1 partby weight, for 100 parts by weight of the alkoxysilane compounds.

Preferably, a dehydrating agent is added to promote the reaction. As adehydrating agent, inorganic compounds such as zeolite, anhydroussilica, and anhydrous alumina, and organic compounds such as methylorthoformate, ethyl orthoformate, tetraethoxymethane, andtetrabutoxymethane can be used. Of these, the organic compounds arepreferred, with ortho esters such as methyl orthoformate, ethylorthoformate being particular preferred. The amount of alkoxysilanecompound bonded with the crosslinkable particles (A) can be determinedas a weight loss (%) when a dry powder is burnt completely in air in athermogravimetric analysis from 110 to 800° C.

The following examples are given as particular embodiments of theinvention and to demonstrate the practice and advantages thereof. It isto be understood that the examples are given by way of illustration andare not intended to limit the specification or the claims that follow inany manner.

EXAMPLES

Several compositions were prepared by admixing components as set forthin Table 1 below. The amounts in Table 1 are in weight percentagesrelative to the total weight of the compositions.

The compositions in Table 1 were coated on a polynorbornene substratesample (Arton®, JSR-Tokyo-Japan) as a 25 micron thick layer and, afterevaporation of solvent during 3 minutes at room temperature, cured underair at 1.0 J/cm² using a Fusion unit equipped with a D lamp. Thedimensions of the polynorbornene substrate, before applying thecomposition, was: length 20 cm, width 5 cm, and thickness 100 microns.

Adhesion was tested according to testing method ASTM D3359, which isherewith incorporated by reference, which uses a rating scale from 0-5,with 5 being the highest adhesion and 0 the lowest.

Flexibility of the coatings was measured by winding the coatedpolynorbornene substrates around rods of different diameter, with thepolynorbornene substrate facing the surface of the rod and,consequently, the coating facing away from the rod, and by subsequentlydetermining the degree of cracking. The results are given in Table 2.The severity of cracks, as determined with the naked eye, is indicatedwith numerals 0-5, with 0 meaning no cracks were observed and 5 meaningvery severe cracking was observed. For instance, the indication 3 meansthat approximately 10 cracks were observed in the outer coating layer ofthe fully wound substrate. The indication “--” means that the coatingwas no longer coherent. TABLE 1 Comparative Examples 1-3 and Examples 1Comparative Comparative Comparative Ingredients Example 1 Example 2Example 3 Example 1 Acrylated MEK-ST (acrylated silica particles 75.0075.00 in methyl ethyl ketone [30 wt % particles relative to the combinedweight of particles and methyl ethyl ketone]) Acrylated MT-ST (acrylatedsilica particles 75.00 72.00 in methanol [30 wt % particles relative tothe combined weight of particles and methanol]) Dipentaerythritolmonohydroxy penta 14.30 13.60 acrylate (SR-399) Tris (2-hydroxyethyl)isocyanurate triacrylate 9.50 22.00 (SR-368) Ethoxylated (9)trimethylolpropane 22.00 9.00 triacrylate (SR-502) Irgacure 184photoinitiator (Ciba Geigy) 1.50 1.50 1.50 1.50 Irgacure 907photoinitiator (Ciba Geigy) 0.90 1.50 1.50 0.90 A-189 silane adhesionpromoter (gamma- 3.00 mercaptopropyltrimethoxysilane, Union Carbide)Properties after cure: Adhesion to polynorbornene (ASTM D3359) 0 0 1 1Pencil hardness of coated polynorbornene HB HB 3B HB substrate

TABLE 2 Flexibility of coatings according to Comparative Example 1-3 andExamples 1 Rod Diameter (mm) Polynorbornene Substrate 6.25 5.00 3.753.10 2.50 1.25 Comparative Example 1 5 — — — — — Comparative Example 2 00 0 0 0 2 Comparative Example 3 0 0 0 0 0 0 Example 1 0 0 0 0 3 —

TABLE 3 Table 3 shows another formulation according to the presentinvention. Ingredients Example 2 Acrylated MT-ST (acrylated silicaparticles in methanol 70.00 [30 wt % particles relative to the combinedweight of particles and methanol]) Dipentaerythritol monohydroxy pentaacrylate (SR-399) 13.60 Ethoxylated (9) trimethylolpropane triacrylate(SR-502) 9.00 Irgacure 184 photoinitiator (Ciba Geigy) 1.50 Irgacure 907photoinitiator (Ciba Geigy) 0.90 Methacryloxypropyl trimethoxy silane5.00

Having described specific embodiments of the present invention, it willbe understood that many modifications thereof will readily be apparentto those skilled in the art, and it is intended therefore that thisinvention is limited only by the spirit and scope of the followingclaims.

1. A curable composition for coating a plastic substrate, saidcomposition comprising: (a) at least one component comprised of a metaloxide bonded to an organic compound, said organic compound having (i) aradiation curable group; and (ii) a group represented by the followingformula (1)

wherein X represents an amine (NH), oxygen (O), or sulfur (S) radical;and Y represents an oxygen (O), or sulfur (S) radical; (b) apoly(meth)acrylate compound; and (c) an adhesion promoter; wherein saidcomposition, after cure, has (a) sufficient adhesion to said plasticsubstrate; (b) a pencil hardness of B or higher; and (c) sufficientflexibility.
 2. The composition of claim 1, wherein said plasticsubstrate comprises at least one plastic selected from the groupconsisting of polynorbornene, polyethyleneterephtalate,polymethylmethacrylate, polycarbonate, polyethersulphone, polyimide, andpolyethernaphtalene.
 3. The composition according to claim 1, whereinsaid plastic substrate comprises polynorbornene.
 4. The compositionaccording to claim 1, wherein said metal oxide comprises at least onemetal selected from the group consisting of silicon, aluminum,zirconium, titanium, zinc, germanium, indium, tin, antimony, and cerium.5. The composition according to claim 1, wherein said metal oxide is asilicon oxide.
 6. The composition according to claim 1, wherein saidcomposition comprises, relative to the total weight of the composition,20-95 wt % of said at least one component.
 7. The composition accordingto claim 1, wherein said composition comprises, relative to the totalweight of the composition, at least 50 wt % of said at least onecomponent.
 8. The composition according to claim 1, wherein saidpoly(meth)acrylate compound comprises at least three (meth)acrylategroups.
 9. The composition according to claim 1, wherein saidcomposition comprises 5-25 wt %, relative to the total weight of thecomposition, of a poly(meth)acrylate comprising three (meth)acrylategroups.
 10. The composition according to claim 1, wherein saidcomposition comprises at least two compounds having at least three(meth)acrylate groups.
 11. The composition according to claim 1, whereinsaid composition comprises an ethoxylated triacrylate.
 12. Thecomposition according to claim 1, wherein said composition comprises apentacrylate.
 13. The composition of claim 12, wherein said compositioncomprises 5-25 wt %, relative to the total weight of the composition, ofsaid pentacrylate.
 14. The composition according to claim 1, whereinsaid adhesion promoter is selected from the group consisting ofgamma-mercaptopropyl trimethoxysilane and methacryloxypropyl trimethoxysilane.
 15. The composition according to claim 1, wherein saidcomposition comprises at least 3 wt %, relative to the total weight ofthe composition, of said adhesion promoter.
 16. The compositionaccording to claim 1, wherein said composition comprises at least 5 wt%, relative to the total weight of the composition, of said adhesionpromoter.
 17. The composition according to claim 1, wherein saidpoly(meth)acrylate compound comprises hydroxy groups and/or carboxylicgroups.
 18. The composition according to claim 1, wherein saidcomposition is absent epoxy-functional compounds.
 19. The compositionaccording to claim 1, wherein the pencil hardness of the composition,after cure, is at least HB.
 20. The composition according to claim 1,wherein a 5-10 micron thick cured layer of said composition has atransparency of at least 65% for light having a wavelength of 400 mm.21. The composition according to claim 1, wherein the compositionexhibits a flexibility such that less than 10 cracks are visible in a5-10 micron thick cured layer of the composition when the composition iscoated on said plastic substrate (length 20 cm, width 5 cm, andthickness 100 microns) and wound around a rod of 3.10 mm diameter withthe plastic facing the surface of the rod and, consequently, the curedlayer facing away from the rod.
 22. The composition according to claim1, wherein the composition, after cure, has an adhesion value of atleast 1 as measured according to ASTM D3359.
 23. An article comprising(a) a substrate comprising at least one plastic selected from the groupconsisting of polynorbornene, polyethyleneterephtalate,polymethylmethacrylate, polycarbonate, polyethersulphone, polyimide, andpolyethernaphtalene; and (b) a coating on said substrate, said coatingbeing obtained by curing the composition according to claim
 1. 24. Thearticle of claim 23, wherein said substrate is corona treated.
 25. Thearticle according to claim 23, wherein said article includes an opticaldisplay.
 26. The article according to claim 23, wherein said articleincludes a liquid crystal display or an organic light emitting diodedisplay.
 27. The article according to claim 23, wherein said articleincludes an optical disc.
 28. A process for preparing a substantiallyflexible coating, said process comprising curing a composition accordingto claim
 1. 29. A display monitor comprising a plastic substrate coatedat least in part with a coating formed by curing the compositionaccording to claim
 1. 30. The display monitor of claim 29 wherein animage is viewed through said coating.